The present invention relates to an arrangement in a fuel injection apparatus.
Common rail injection systems utilizing pressure accumulators are currently commonly used in connection with piston engines. In such systems the fuel stored in injection pressure in the so-called pressure accumulator is injected into the combustion chamber of the engine by controlling the injector valve.
Generally, a flow fuse is used as a safety means in injection systems. The flow fuse is usually arranged between the pressure accumulator and the injection valve. The flow fuse closes the flow path from the accumulator in case of a leak and in case the injection valve is stuck, for example, in the open position, in which case there's a situation when fuel can uncontrollably leak into the cylinder combustion chamber. To avoid this situation, U.S. Pat. No. 3,780,716 and WO 95/17594 disclose a flow fuse restricting the fuel flow volume. Typically the flow fuse includes a cylinder space that further includes a piston apparatus having a spring load acting against the fuel flow direction during injection. During normal action the fuel volume needed for each injection corresponds with the volume displaced by the piston. If, for some reason, the injection valve starts to leak, the piston will move to its other limit position, where it will close the flow.
In a typical common rail system the injection pressure reaches a high pressure level almost instantaneously when the needle of the injector nozzle opens. As a result of this, the fuel mass flow is great right at the beginning of the injection during injection of fuel into the combustion chamber. In such a case the pressure in the combustion chamber can increase too fast for reaching optimum performance.
An aim of the present invention is to produce an arrangement in the fuel injection apparatus minimizing the problems associated with prior art. It is an especial aim of the invention to produce an arrangement for restricting the fuel mass flow in the beginning of the injection phase.